Method for producing rectangular hysteresis loop materials



United States Patent 3,113,055 METHOD FOR PRODUCING RECTANGULAR HYSTERESIS LOOP MATERIALS Albert I. Schindler, Adelphi, and Edward I. Salkovitz, Forest Heights, Md., assignors to the United States of America as represented by the Secretary of the Navy Filed Oct. 14, 1960, Ser. No. 62,813 2 Claims. (Cl. 148-103) (Granted under Title 35, US. Code (1952), see. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates to a method for treating high permeability ferrimagnetic and ferromagnetic materials to impart to them the property of exhibiting a rectangular hysteresis loop.

Rectangular hysteresis loop materials are known to be useful in the operation of magnetic memory devices and computers. They have been made from high permeability nickel-iron alloys by annealing the alloy while in a magnetic field. They have also been made by cold rolling of the alloy to tapes of thicknesses under one thousandth of an inch and then annealing. These methods have the disadvantage that they are limited in respect to the alloys which respond to the treatment. The cold rolling method has the further disadvantages that it is laborious and does not give a completely satisfactory material. Additionally, the packing fraction for thin tapes is low.

It is an object of the present invention to provide a new method for treating ferrimagnetic and ferromagnetic materials of high permeability to cause them to exhibit a rectangular hysteresis loop.

The above and other objects of the invention can be accomplished by the method of our invention which comprises subjecting the material of high magnetic permeability, which may be a nickel-iron alloy or a :ferrite, to irradiation with neutrons While in a saturating magnetic field.

High permeability nickel-iron alloys of widely varying nickel and iron content may be treated by the method of our invention for the development of a rectangular hysteresis loop therein. The nickel content of the alloys may range from about 40 to 90% by weight and the iron content from about to 60% by weight. The alloys may also contain up to a total of about 10% by weight of one or more elements which increase the magnetic permeability of the alloy, such as molybdenum, copper, chromium, manganese and silicon. Among such nickeliron alloys are, for example, those of the following composition by Nveight: 50% Ni-50% Fe; 48% Ni52% Fe; 79% Ni17% l e-4% Mo; 47% Ni-50% Fe3% Mo; 78% Ni-% Fe-5% Cu2% Cr; 65% Ni-25% Fel0% Mn and 43% Ni-54% Fe-3% Si, etc. Ferrimagnetic materials which may be treated by the method of our invention for the development of a rectangular hysteresis loop therein are, for example, the ferrites or spinels containing the following metal oxides: MnO. ZnO. Fe O and NiO. ZnO. CuO. Fe O etc.

In the practice of the method of invention, the magnetic material to be treated is mounted on a suitable sup- Patented Dec. 3, 1963 port and is supplied with a saturating magnetic field, for example, by a winding of adequate capacity which is wound thereon. The Winding is provided with means for connecting it to an A.C. or DC). current supply. The assembly is placed in a metal can and positioned in the reactor and, with control of the temperature at a selected low level, not above about 250 C., irradiation of the magnetic material is conducted While a magnetizing current is passed through the Winding around the material.

The method of the invention is illustrated by the application of it to commercially available nickel-iron alloy toroids in which the alloys were of the following compositions by weight:

1. 79% Ni17% Fe4% Mo (permalloy) 2. 79% Ni-16% Fe-5% Mo 3. 78% Nil5% Fe5% Cu (mumetal) 4. 48% Ni52% Fe Two toroids of the same alloy composition were used in each instance. They were wound with appropriate B and H coils and installed on the same holder, which may be a metal rod. Pre-irradiation 60 cycle hysteresis loop measurements were taken for the toroids after which they were positioned in the reactor (Brookhaven) and irradiated with neutrons for two weeks. The total integrated flux for the treated toroids was 5 fast=1.25 10 to 3.0)(10 nvt thermal=5.9 10 mt while the temperature during irradiation was kept relatively constant, the limits being between 80 C. and C. During the irradiation, a saturating direct current was passed through the H-coil of the one toroid of each pair of the toroids. The field produced was in the same direction as the field applied during hysteresis loop measurements. After the irradiation, the hysteresis loops of each toroid was again taken.

The preand post-irradiation hysteresis loops of the permalloy and mumetal alloys obtained as the result of the application of the method of the invention as described above are shown in FIG. 1 and FIG. 2, respectively, of the accompanying drawing and are illustrative of the efiicacy of the method to cause the development of a rectangular hysteresis loop in magnetic materials as defined herein. In the figures, B is in kilogauss and H in oersteds. The pre-irradiation hysteresis loops are marked a, and the post-irradiation hysteresis loops, b and c. Loop b is the hysteresis loop of the alloy irradiated in the absence of a magnetic field, whereas loop 0 is that for the alloy irradiated in the presence of a saturating magnetic field applied to the toroid. In both cases, the loop b exhibits decreased remanence, increased coercive force and decreased permeability for the alloy in contrast to the non-treated alloy. In loop c, a strikingly diflerent effect was observed, namely, square loop characteristics were obtained with both the coercive [force and remanence increasing.

The above method is also applicable to the development of a rectangular hysteresis loop in ferroelectric materials, e.g., barium titanate, with the modification that the ferroelectric material is irradiated with neutrons while in a high intensity electric field instead of in a saturating magnetic field.

While the invention has been described herein with refernce to certain specific embodiments, it is to be understood that such are to be taken by way of illustration and not in limitation on the scope of the invention except as may be defined in the appended claims.

What is claimed is:

1. A method of treating a magnetic nickel-iron alloy of high permeability which comprises subjecting the nickel-iron alloy to irradiation with neutrons in a saturating magnetic field at a temperature between about 80 and 250 C. until it exhibits a rectangular hysteresis loop.

2. method of treating a magnetic nickel-iron alloy 4 r of high permeability which comprises subjecting the nickel-iron alloy to irradiation with neutrons in a saturating magnetic field at a temperature between about 80 and 120 C. until it exhibits a rectangular hysteresis loop.

Schindler et al.: Journal of Applied Physics, Vol 30, No. 4, pages 282 S and 283 S, April 1959. 

1. A METHOD OF TREATING A MAGNETIC NICKEL-IRON ALLOY OF HIGH PERMEABILITY WHICH COMPRISES SUBJECTING THE NICKEL-IRON ALLOY TO IRRADIATION WITH NEUTRONS IN A SATURATING MAGNETIC FIELD AT A TEMPERATURE BETWEEN ABOUT 80 AND 250*C. UNTIL IT EXHIBITS A RECTANGULAR HYSTERESIS LOOP. 